@article {Stubbs017756, author = {Alexander L. Stubbs and Christopher W. Stubbs}, title = {A Novel Mechanism for Color Vision: Pupil Shape and Chromatic Aberration Can Provide Spectral Discrimination for {\textquotedblleft}Color Blind{\textquotedblright} Organisms}, elocation-id = {017756}, year = {2015}, doi = {10.1101/017756}, publisher = {Cold Spring Harbor Laboratory}, abstract = {The only known mechanism for color vision requires spectrally diverse photoreceptor types (1). However color vision typically comes at a cost: a reduction in signal to noise ratio in low light conditions and degraded angular resolution in each spectral channel. Coleoid cephalopods (octopus, squid, cuttlefish) have a single photoreceptor type (2,3,4) and lack the ability to determine color by comparing detected photon intensity across multiple spectral channels. Nevertheless, cephalopods produce vividly colorful mating displays and use adaptive camouflage to match the color of their natural surroundings. This presents a paradox - behaviors that imply an ability to determine color in organisms with a monochromatic visual system - that has long puzzled biologists (5,6,7). Here we propose a novel mechanism for spectral discrimination: the exploitation of chromatic aberration (wavelength-dependence of focal length) by organisms with a single photoreceptor type. Through numerical modeling we show how chromatic aberration can yield useful chromatic information via the dependence of image acuity on accommodation. The peculiar off-axis slit and annular pupil shapes in these animals enhance this chromatic signature. Our model is consistent with existing data on cephalopod behavior and retinal morphology. This principle has broad applicability in other organisms, such as spiders and dolphins.}, URL = {https://www.biorxiv.org/content/early/2015/04/22/017756}, eprint = {https://www.biorxiv.org/content/early/2015/04/22/017756.full.pdf}, journal = {bioRxiv} }